Pig Health - Seasonal Infertility

Like many species the domesticated pig still retain some
elements of seasonality in its breeding cycle but 2 distinct
patterns can be discerned which can reduce fertility leading to
lost production, uneven farrowing patterns and disruption to the
overall management of the commercial unit.

Successful service represents the start of the production cycle
of the pig farm and is thus key to production; any disruption to it
has a cascading effect throughout the farm.

Fig 2: Indoor systems however can be vulnerable to the weather
and lighting patterns

Fig 3: Any sow house exposed to natural lighting can be
vulnerable to the rapid decrease in day length that occurs in
autumn

Fig 4: Minimal natural lighting allows control of light
patterns making the herd less vulnerable to autumn infertility

Firstly problems may occur in early to mid summer (June-August)
as a result of high temperatures. Whilst outdoor herds and
those in southern sheltered areas may be more vulnerable,
temperatures in buildings of over 30ºC are not uncommon
sporadically throughout the UK. This appears to have several
potentially damaging effects:-

Where such temperatures are expected dampening floors or even
the outside roof can cool buildings but adequate insulation and
ventilation will go a long way to offset high air
temperatures. Plenty of cold drinking water should also be
available and where appropriate, wallowing areas can help.
However, with outdoor sows, wallows in farrowing pens should be
avoided as they encourage litter desertion. It may also be
appropriate to reduce the amount of bedding material to increase
heat dissipation.

Secondly, each year, some farms suffer from a drop in fertility
levels in later summer/early autumn, which appears to be unrelated
to either infectious disease or husbandry factors. This is
usually termed autumn or seasonal infertility but can almost run on
from summer (hot weather) infertility. It represents a biological
reaction to changing climatic conditions through the year and is
thus more of a natural consequence for the pig than adverse
reactions to heat.

Presentation

The key features of autumn infertility are:-

1) Young breeding animals and particularly gilts are more likely
to be affected than older sows.

2) It can present as a delay in onset of oestrous, complete
failure to cycle or an in increase in returns to service - usually
at regular 3 week intervals. Abortion in later pregnancy is
not uncommon.

3) In a typical year, the problem starts in mid September
and runs through to late October - specifically sows and gilts
served at this time.

4) In years where a poor summer has been experienced the effect
may occur 2-3 weeks earlier than usual and will tend to be more
widespread.

5) Some farms are particularly vulnerable, seeing some evidence
every year, whilst others may only see the effect every few years
or never.

Cause

A number of factors have been proposed that may trigger the
problem.

1) Most significant is lighting patterns. During the high
risk period, the day length is decreasing at its most rapid rate -
approximately 30 minutes per week of daylight is lost for each day
during this time. This is believed to have an effect on a complex
chain of hormones produced in the brain which "shut down" the
reproduction system. It seems likely that a summer of low
light levels reduces the "start point" of the sow as day length
starts to decrease, offering an explanation for higher and early
incidence after poor summers.

2) Day/night temperature variation tends to increase in the
autumn. The pig is poor at controlling body temperature and
it is suggested that a chilling effect will occur in a cool night
following a warm day, leading to a deficit in blood sugar.
This will have the effect of reducing the levels of insulin
released, which act as a trigger to the reproductive cycle.

3) Sunspot activity which induces ionising radiation is high in
the autumn (as indeed it is in spring) and this has been suggested
as one of the more obscure factors in triggering autumn
infertility.

It is relevant to point out that the wild pig is a seasonal
breeder, not designed to produce a litter in the depths of
winter. It is widely believed that autumn infertility is a
throw back to nature triggered by environmental factors.

Farrowing rates can drop by 15-20% in severely affected herds
leading to a drop in numbers of sows farrowing at the end of the
year and often a consequential surge in production following this
as returns are reserved.

Control and Prevention

In the indoor herd, lighting levels can be controlled, although
many sow houses now tend to be more heavily influenced by natural
light than was the case in the days of stalls and tethers. A
day length of 14-16 hours lighting appears to be advantageous in
reducing the diminishing natural light but this must be provided
from earlier in the summer - beginning of August at the latest - to
be wholly effective. The light should be sufficient at pig
level to be able to read small newsprint (so make sure your pigs
can read!).

This clearly cannot be done in the outdoor environment.

Feed levels should be increased for all weaned and served sows
by 0.25-0.5kg per head per day from early September, unless plenty
of good quality barley straw is available which will supply
increasing energy needs.

There may be a benefit of increasing boar contact with gilts and
sows after service during the danger period - the boar is believed
to have a stimulating effect on the establishment of
pregnancy. This contact should be physical - not just fence
line - and intermittent for 20-30 minutes every 24 hours.

In herds known to be vulnerable to autumn infertility -
particularly those outdoors - it is common practice to reduce
culling of older sows and increase gilts services in late summer,
early autumn to offset the drop in fertility and, hence, aim to
maintain farrowing targets towards the end of the year, thus
maintaining breeding herd output and ultimately baco sales in early
spring and mid-summer.

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